1. Field of the Invention
The present invention relates to a solid wire for carbon dioxide gas shielded arc welding which has no copper plating on the wire surface, and more particularly to a non-copper-plated solid wire for carbon dioxide gas shielded arc welding which has improved wire feeding property or feedability, resulting from controlling the roughness and micro-hardness of the wire surface.
2. Description of the Related Art
Recently, with the introduction of automatic welding systems, a solid wire for carbon dioxide (CO2) gas shielded arc welding has widely been used in the fields of, in particular, steel frames, automobiles, ship and building construction.
As for a solid wire for such CO2 gas shielded arc welding, it is usual to use a so-called copper-plated solid wire wherein copper is plated on the wire surface. The reason why copper is plated is to improve electric conductivity, wire feedability and corrosion resistance.
Due to the friction between a wire and a drawing die occurring in a drawing process at the time of wire manufacturing, a portion of copper plating is peeled away from the wire surface, and another portion of copper plating is deposited in the form of copper dust on dents of the wire surface.
During a welding operation, the copper dust falls from the wire surface and accumulates on a welding tip due to the friction between the wire and the welding tip. As a result, the welding tip is clogged, thereby causing welding instability and generating a large amount of spatters.
In addition to the copper dust, the copper plated wire has the following problems:
(1) The copper plating layer is more soft than the wire surface and thus the copper plating is inevitably peeled off from the wire surface due to the friction between the wire and the welding tip, thereby causing welding instability.
(2) Copper has a low melting point of 1,083° C. and thus is liable to be vaporized at a ultra high temperature during a welding operation, thereby generating a large amount of fumes.
In spite of these disadvantages of copper plated wires, copper plating on a wire surface has been considered to be inevitable for the purpose of improving electric conductivity.
In view of the foregoing, it is necessary to develop non-copper-plated wires capable of satisfying various characteristics including advantageous characteristics of copper-plated wires.
Meanwhile, wires without copper plating have been proposed, for example in Japanese Patent Registration No. 2682814 (arc welding wire), Japanese Patent Application Laid-Open Publication No. Hei.11-147174 (non-plating welding wire for steel) and 2000-94178 (welding wire without plating). These prior arts propose the use of at least one kind of lubricating powder such as MOS2, WS2, and C or the coating of lubricating oil on a wire surface, for the purpose of improving wire feedability.
Japanese Patent Application Laid-Open Publication No. 2000-117484 discloses a welding wire, on the wire surface, having a wavy part of ruggedness of a predetermined wavelength along the circumferential direction, which is excellent in an arc starting property, resulting from controlling peak intensity measured in the power spectrum to a desired value. Japanese Patent Application Laid-Open Publication No. 2000-317679 discloses a non-plating wire for arc welding and an arc welding method, in which an insulating inorganic powder having a small average grain diameter and an electrically conductive inorganic powder are stuck on the welding wire surface in predetermined amounts using water soluble macromolecule, thereby generating a reduced amount of fumes or spatters.
In addition, Japanese Patent Application Laid-Open Publication No. Hei.11-342494 discloses a solid wire for carbon dioxide gas arc welding, in which wire components, C, Si and Mn involved in spatter generation satisfy the following relationship: (10C+2Si+Mn)=2.4 to 5.25 wt %, thereby generating a reduced amount of spatters.
The above wires have improvements as non-copper-plated wires but do not satisfy all characteristics desired as welding wires. In particular, in the case of coating fine powders on the wire surface in order to improve the properties of non-copper-plated wires, the powders coated on the wire surface inevitably causes the generation of fumes. Furthermore, because it is difficult to control the amount of the powders to be coated to an appropriate level, the powders are not uniformly coated on the wire surface, thereby generating an increased amount of spatters.
Meanwhile, in automatic welding, feedability of a welding wire is defined as the length of the wire emerging from the front end of a welding tip relative to that of the wire fed by the rotation of a feeding roller. Poor feedability may increase the length of arc and fluctuate a welding current in welding operation, thereby generating an increased amount of spatters.
In this regard, the amount of generated spatters may be used as a standard reflecting feedability of the welding wire.